Marvin Lee Wilson, a man with an IQ of 61, was executed Aug. 7 by the Texas Department of Corrections after the Supreme Court rejected an appeal on the grounds that he was mentally impaired and thus ineligible to be sentenced to the death penalty.

Wilson’s lawyers were upset at the Supreme Court’s ruling and Texas law, which they say is outdated and not in line with what many leading experts in mental disabilities believe should be the standard to measure competency.

“It is outrageous that the state of Texas continues to utilize unscientific guidelines to determine which citizens with intellectual disability are exempt from execution,” Wilson’s attorney, Lee Kovarsky, told The Houston Chronicle. “(The guidelines) are not scientific tools; they are the decayed remainder of an uninformed stereotype that has been widely discredited by the nation’s leading groups on intellectual disability.”

Wilson was convicted of the 1992 murder of 21-year-old police informant Jerry Robert Williams. He was sentenced to death in 1994.

According to The Huffington Post, Wilson claimed that he didn’t commit the murder, and argued that his mental hindrances should prohibit him from receiving the death penalty. His claims of mental deficiencies were supported by school records, in which he received failed 7th grade and received D’s and F’s, according to the Huffington Post.

Wilson took an IQ test in 2004, and was given a score of 61. His attorneys argued that the Supreme Court should use precedent it set in 2002 which considered the execution of the mentally retarded as cruel and unusual punishment.

However, neither Texas nor the Supreme Court bought the argument.

Prosecutors in the case said that Wilson’s ability to survive on the streets and orchestrate the crime of which he was convicted proved that his defense was not valid.

“Considering Wilson’s drug-dealing, street-gambler, criminal lifestyle since an early age, he was obviously competent at managing money, and not having a 9-to-5 job is no critical failure,” Edward Marshall, a Texas assistant attorney general told The Associated Press. “Wilson created schemes using a decoy to screen his thefts, hustled for jobs in the community, and orchestrated the execution of the snitch, demonstrating inventiveness, drive and leadership.”